PIEZO1 and hydrops fetalis: In the OL of the TMJ from HF group, the MS-ion channel PIEZO1 was expressed in cells within the fibrous layer and in the proliferating chondrocytes underneath (Figs. 1A, a1; S1), while a few TRPV4 positive cells were observed in the OL (Figs. 2A, a1; S1).